Human Relevance of Viruses

The economic impact of viruses in both third-world and industrialized countries is enormous. The annual loss in work time due to common cold and influenza viruses alone amounts to millions of hours. While discomfort, adverse effects on employment, and even deaths due to viral diseases, such as chicken pox, measles, German measles, mumps, and yellow fever, have declined dramatically since immunizations against the diseases became widespread, they still take their toll. Another viral disease, infectious hepatitis, periodically still claims victims. Guillain-Barre syndrome and Epstein-Barr are debilitating diseases caused by viruses that are apparently carried by nearly everybody, but what triggers them into action is as yet still unknown.

The virus associated with AIDS (acquired immune deficiency syndrome), a usually fatal disease, is caused by a retrovirus (a virus with two identical single nuclear strands) that is related to those that cause cancer. It was detected in a blood sample collected in 1959 from Zaire. AIDS was not adequately described, however, until 1981, and the virus itself was not identified until 1983. Research has shown that two forms of the AIDS virus, HIV-1 and HIV-2, diverged from a common ancestor in the early 1950s (Fig. 17.19). Thirty years later, the AIDS virus had spread all over the world. Retroviruses mutate so rapidly that they are capable of evolving about a million times faster than cellular organisms. Since the initial appearance of AIDS, increasing research is being applied to the development of a vaccine with the use of a genetically engineered virus. If successful, the vaccine will cause the human body to develop a defense against AIDS viruses without the disease itself developing.

The production of vaccines for a number of other diseases is undertaken by a flourishing worldwide multimillion dollar industry. Other mass-produced viruses are used to infect ticks, insects, and other disease organisms of both animals and plants. Some viruses cause great losses when they infest creamery vats during the manufacture of dairy products or culture vats during the production of antibiotics. One phage attacks nitrogen-fixing bacteria in the roots of leguminous plants, while other phages attack diphtheria and tuberculosis bacteria. One natural virus called Abby (an abbreviation of Abington, which is one of 19 strains of nuclear polyhedrosis viruses) is found only in the caterpillars of gypsy moths. Gypsy moth caterpillars have been

Kingd om Bacteria, Kingdom Archaea, and Viruses 321

lipid membrane envelopoe glycoprotein 41

glycoprotein 41

Nuclear Polyhedrosis Virus

Figure 17.1Q A virus is a nucleic acid coated with protein. The human immunodeficiency virus (HIV), which causes AIDS, consists of RNA surrounded by several layers of proteins. Once inside a human cell (usually a T cell, part of the immune system), the virus uses an enzyme to convert its RNA to DNA, which then inserts into the host DNA. HIV damages the human body's protection against disease by killing T cells and by using these cells to make more of itself.

Figure 17.1Q A virus is a nucleic acid coated with protein. The human immunodeficiency virus (HIV), which causes AIDS, consists of RNA surrounded by several layers of proteins. Once inside a human cell (usually a T cell, part of the immune system), the virus uses an enzyme to convert its RNA to DNA, which then inserts into the host DNA. HIV damages the human body's protection against disease by killing T cells and by using these cells to make more of itself.

particularly destructive in forests of both North America and Europe, and it is hoped that the destruction may be greatly reduced by the dissemination of this virus in the forests under attack.

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  • attilio
    How a virus attacks the human body?
    6 years ago

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